Novel method to meassure fine particle circulation rates in draft tube conical spouted beds

The spouted bed regime is an alternative contact method to fixed and fluidized beds. The ratio between the inlet diameter and particle diameter limits the scaling-up of spouted beds (the inlet diameter should be smaller than 20-30 times the particle diameter). The insertion of a draft tube is the way of overcoming this limitation. Particle cycle time is defined as the time the particle takes to travel from the top of the annulus downwards and back again to its starting point. Since the proportion of time spent by a particle in the spout is insignificant compared with that spent in the annulus, particle cycle times can be deduced from solid flow patterns in the annulus (1). Knowledge of particle cycle time is very useful to ascertain the bases of the spouted bed technique. Furthermore, information on this parameter and particle trajectories is essential for spouted bed applications, given that the average cycle time regulates energy and mass transfer, and influences chemical reactions (2). The most used technique to measure the solid cycle times is particle tracking, but monitoring of fine particles requires very sofisticated techniques, whose reliability is open to debate. Accordingly, the main aim of this work is to setup a device and develop a methodology for measuring the circulation rate of fine particles in conical spouted beds. The device is a sector located on the upper surface of the annulus, which collects the particles raining down in the fountain. Based on the information gathered, the factors of major influence on the solid circulation rate are determined and their effect is quantified. The material used for operation is building sand of0.6 mmparticle diameter, but glass beads (coarse particles) of4 mmdiameter have also been used so as to verify the methodology proposed by comparing the results with those obtained by monitoring a marked (painted) particle. REFERENCES 1. N. Epstein, J.R. Grace. Eds. Cambridge University Press: New York, 2011. 2. J. Makibar, A.R. Fernandez-Akarregi, I. Alava, F. Cueva, G. Lopez and M. Olazar. Investigations on heat transfer and hydrodinamics under pirolisis conditions of a pilot-plant draft tube conical spouted bed reactor. Chem. Eng. Process., 50: 790-798, 2011

STUDY OF THE MINIMUM SPOUTING VELOCITY IN A DRAFT TUBE CONICAL SPOUTED BED

A study has been carried out on the hydrodynamics of conical spouted beds with a non-porous draft-tube. A hydrodynamic correlation has been proposed for calculating the minimum spouting velocity as a function of dimensionless moduli that take into account geometric factors, particle characteristics and operating conditions. A statistical analysis of the data obtained following a design of experiments shows that the inlet diameter, particle diameter and the height of the entrainment zone are the parameter of greater influence on the minimum spouting velocity

Correlation of the Minimum Spouting Velocity for the Design of Open-Sided Draft Tube Conical Spouted Beds for the Treatment of Fine Materials

The hydrodynamics of conical spouted beds provided with open-sided draft tubes have been studied for the treatment of fine particles. A correlation has been proposed for the calculation of the minimum spouting velocity as a function of dimensionless moduli that take into account the geometric factors of the contactor and the draft tube, particle characteristics and operating conditions

A neural-based modelling approach to estimate residence time and solids flow rate in a conical spouted bed with and without draft tubes

Spouted beds are an alternative contact method to the fixed and fluidized beds especially for handling coarse particles. Since its discovery in 1954 by Gishler and Mathur during grain drying in a fluidized bed, spouted beds have been widely studied and applied in different industrial processes, such as, particle coating, catalytic reactors, pyrolysis and drying of solids, pastes and suspensions. One of the main advantages of spouted beds over fluidized beds is its high degree of mixing between gas and solids within the bed due to a cyclical and uniform movement of particles, leading to high heat and mass transfer rates and also a homogeneous final product. Despite its advantages, the conventional configuration of the spouted bed still has some limitations; such as a high pressure drop for stable spouting, the existence of a maximum height for a stable spout with the corresponding scaling-up limitations and the highly dependable gas flow rates on stable spouting. In order to minimize these operational limitations, several spouted bed configurations have been proposed, the main ones being the spouted bed with a draft tube, the two-dimensional spouted bed and the spouted bed with supplementary aeration, among others. Solids residence time and flow rates are key parameters in the modeling, optimization and control of any process. Although predictions of solids residence time and flow rate are important issues that reflect the accuracy of the whole process simulation, difficulties arise in the use of either purely mechanistic or empirical approaches. In developing a reasonable theoretically based model, the only task is to estimate the values of the coefficients in the model, but, taking into account all relevant phenomena involved this model can prove to be impractical. Additionally, the seemingly overwhelming choice of structural options for empirical models may considerably hinder the modeling step. Artificial neural networks may be an effective alternative in that they can represent highly nonlinear processes, with flexibility and robustness against input noise and once they have been developed and their coefficients determined, they can provide a rapid response for a new input [1]. This neural network based model (MatLab® R2013a, Mathworks) uses the particle diameter dp, bed density ρb, cone angle γ, inlet diameter D0 and draft tubes characteristics as inputs whilst the maximum, mean and minimum residence times along with the solid flow rates are predicted with reasonable agreement with the experimental data, as shown in Figure 1 Please click Additional Files below to see the full abstract

A CONICAL SPOUTED BED REACTOR FOR THE VALORISATION OF WASTE TIRES

A pilot plant provided with a conical spouted bed reactor has been used for the valorisation of waste tires by thermal pyrolysis in continuous mode. The effect of pyrolysis temperature on product distribution and properties has been studied in the temperature range from 425 to 600 ºC. This variable has proven to have an important effect on product distribution. Thus, pyrolysis oil yield was reduced from 64.3 wt% at 425 ºC to 55.9 wt% at 600 ºC. However, the quality of carbon black was improved operating at high temperatures (increasing BET surface area values). High yields of certain interesting chemicals have been obtained in the liquid fraction, such as limonene (19.3 wt%), isoprene (5.7 wt%) and styrene (6.1 wt%)

Biomasa hondakinak balioztatzeko prozesu motak

Lan honetan biomasa hondakinak balioztatzeko prozesu nagusiak aztertu dira. Alderaketaren ardatzak honelakoak izan dira: lehengaiaren hezetasuna, erreakzioa burutzeko baldintzak (batik bat, konbertsio-denbora eta tenperatura), lortutako produktuak eta teknologiaren heldutasuna. Biomasa balioztatzeko erabiltzen diren teknologiak bi talde nagusitan banatu daitezke: Termokimikoak eta biokimikoak. Konbertsio termokimikoan oinarritzen diren prozesu nagusiak errekuntza, gasifikazioa, torrefakzioa eta pirolisia dira. Erreakzioak tenperatura altuan egiten direnez, konbertsio-denbora baxua izan ohi da. Komenigarria da prozesu hauetan lehengai lehorrak (basogintza, nekazaritza eta abeltzaintza ustiaketetako hondakinak eta papergintza industriako hondakinak) erabiltzea. Bestalde, prozesu biokimiko edo biologikoetan, mikroorganismoek erreakzioan parte hartzen dute eta lehengai hezeak erabiltzen dira: mindak, gorotzak, araztegietako hondakin uren lohiak eta elikadura-industriako hondakin organikoak. Prozesu nagusiak konpostatzea, digestio anaerobikoa eta hartzidura alkoholikoa dira. Tenperatura baxua izaten da (70ºC baino baxuagoa) eta ondorioz, erreakzio-denbora luzea eta bolumen handiko erreaktorea behar da. Erreakzioak burutzeko, egunak (hartzidura alkoholikoan), asteak (digestio anaerobikoan) edo hilabeteak (konpostatzearen kasuan) behar dira

Bed symmetry in the fountain confined conical spouted beds with open-sided draft tubes

Bed symmetry has been analysed in fountain confined conical spouted beds operating with fine particles. Thus, vertical particle velocities and the spout shape have been determined in a wide range of spouting air velocities and bed configurations. Bed symmetry is widely accepted in the spouted beds without draft tubes or with nonporous ones, but this is not the case when open-sided draft tubes are used. Thus, radial particle velocity profiles differ depending on the cross-sectional angular plane considered in the open-sided draft tubes. The spout expands preferentially along the tube opened surface, and is wider as spouting air velocity and aperture ratio are increased. The literature correlations proposed for the average spout diameter have been analysed and no one is valid for estimating this parameter in the whole range of spouting air velocities and configurations analysed in these systems operating with fine particles.This work has received funding from Spain's Ministry of Science and Innovation (PID2019-107357RB-I00 (AEI/FEDER, UE)), the Basque Gov- ernment (IT1218–19 and KK-2020/00107) and the European Commis- sion (HORIZON H2020-MSCA RISE-2018. Contract No.: 823745). M. Tellabide thanks Spain's Ministry of Education, Culture and Sport for his Ph.D. grant (FPU14/05814). I. Estiati thanks the University of the Basque Country for her postgraduate grant (ESPDOC18/14)

Biomasa hondakinak balioztatzeko prozesu motak

Lan honetan biomasa hondakinak balioztatzeko prozesu nagusiak aztertu dira. Alderaketaren ardatzak honelakoak izan dira: lehengaiaren hezetasuna, erreakzioa burutzeko baldintzak (batik bat, konbertsio-denbora eta tenperatura), lortutako produktuak eta teknologiaren heldutasuna. Biomasa balioztatzeko erabiltzen diren teknologiak bi talde nagusitan banatu daitezke: Termokimikoak eta biokimikoak. Konbertsio termokimikoan oinarritzen diren prozesu nagusiak errekuntza, gasifikazioa, torrefakzioa eta pirolisia dira. Erreakzioak tenperatura altuan egiten direnez, konbertsio-denbora baxua izan ohi da. Komenigarria da prozesu hauetan lehengai lehorrak (basogintza, nekazaritza eta abeltzaintza ustiaketetako hondakinak eta papergintza industriako hondakinak) erabiltzea. Bestalde, prozesu biokimiko edo biologikoetan, mikroorganismoek erreakzioan parte hartzen dute eta lehengai hezeak erabiltzen dira: mindak, gorotzak, araztegietako hondakin uren lohiak eta elikadura-industriako hondakin organikoak. Prozesu nagusiak konpostatzea, digestio anaerobikoa eta hartzidura alkoholikoa dira. Tenperatura baxua izaten da (70ºC baino baxuagoa) eta ondorioz, erreakzio-denbora luzea eta bolumen handiko erreaktorea behar da. Erreakzioak burutzeko, egunak (hartzidura alkoholikoan), asteak (digestio anaerobikoan) edo hilabeteak (konpostatzearen kasuan) behar dira

Effect of operating conditions on the hydrodynamics in fountain confined conical spouted beds

La estabilidad y el funcionamiento de los spouted beds se ven muy afectados por las características de las partículas. En consecuencia, se ha estudiado el comportamiento hidrodinámico de los spouted beds cónicos para partículas finas que difieren en tamaño y densidad en una amplia gama de caudales de aire de entrada. Este conocimiento es esencial para un exitosa escalado e implementación industrial del del spouted bed. Por lo tanto, se ha determinado el efecto que tienen la velocidad del aire y las propiedades del sólido (densidad y tamaño) sobre la velocidad local del sólido en un spouted bed de fuente confinada utilizando una técnica de boroscopio (Velocimetría de seguimiento de partículas, PTV) aplicada a varias configuraciones de lecho. Los resultados muestran una estrecha relación entre la velocidad del aire de entrada y la velocidad local del sólido, siendo el contacto gas-sólido especialmente vigoroso en las configuraciones sin tubo y con tubo central de aberturas. El caudal de circulación de sólidos es más bajo cuando se utiliza un tubo central no poroso debido a las bajas velocidades verticales de los sólidos en la zona anular, incluso con caudales de aire altos. Sin embargo, las velocidades verticales en la zona anular aumentan cuando aumentan el tamaño y la densidad de las partículas, aunque estas velocidades son menores en las regiones de spout y la fuente debido al mayor intercambio de momento requerido para su aceleración.Este trabajo ha recibido financiación del Ministerio de Ciencia e Innovación de España (PID2019-107357RB-I00 (AEI/FEDER, UE)), del Gobierno Vasco (IT1218-19 y KK-2020/00107) y de la Comisión Europea (HORIZON H2020-MSCA RISE-2018.Nº de contrato: 823745). M. Tellabide agradece al Ministerio de Educación, Cultura y Deporte de España su beca de doctorado (FPU14/05814). I. Estiati agradece a la Universidad del País Vasco su beca de posgrado (ESPDOC18/ 14)